Nano-and Micro-Actuations of Hard Disk’s Head Positioning System: Precision Control and Evaluation

A new piezoelectric micro-actuator with 2-dimensional control, i.e., a track following control and a flying height control, of the head positioning system for high-density hard disk drives (HDD) was previously developed in our lab. In this study, control algorithms for the new 2-degree-of freedom (DOF) micro-actuator are developed to independently control the lateral displacement and the transverse deflection to against various disturbances and system uncertainties. The structure of the piezoelectric micro-actuator is reviewed briefly. Then, the overall control strategy for the micro-actuator system is discussed. Next, controller design schemes for each DOF are presented. The pole placement method is used to design controllers. To obtain compensation for overshoot and settling time, pole and zero locations are carefully chosen. First, the control law is defined for the disturbance rejection. Second, the estimator is designed for noise reduction. Lastly, the reference input is added for the command following. Simulation results show that the proposed controllers in the closed-loop system provide good stability, and compensate for disturbances and noises. The data suggest that the proposed micro-actuator control system considerably improves track following and flying height control of head positioning systems in highdensity HDDs.